1. Field of the Invention
This invention relates to a dual pipette device for drawing two different liquids thereinto by suction and ejecting the liquids therefrom. This invention particularly relates to a dual pipette device suitable for feeding a sample solution and a reference solution by spotting to a slide type ionic activity measuring device.
2. Description of the Prior Art
As disclosed in, for example, Japanese unexamined patent publication Nos. 58(1983)-211648 and 59(1984)-30055 and Japanese patent application No. 59(1984)-11744, there has been proposed an ionic activity measuring device for receiving an aqueous liquid sample, for example, a wine, a beverage, service water, particularly a body fluid (blood, urine, saliva or the like), which is fed by spotting, and quantitatively analyzing the activity or concentration of a predetermined ion contained in the sample by potentiometry.
In general, the ionic activity measuring device is provided with at least one set of ion selective electrode pairs having an ion selective layer selectively responding to a predetermined ion as the outermost layer. In the disclosures referred to above, the ion selective electrode pair is supported between an upper frame and a lower supporting frame. The upper frame is provided with a pair of liquid access holes positioned to correspond to the set of the ion selective electrode pair. A porous bridge (preferably constituted by twisted fiber yarn) is disposed, usually on the upper frame, for achieving electrical conduction through liquid junction between sample liquid fed to one of the pair of the liquid access holes and reference solution fed to the other. In the case where multiple sets of the ion selective electrode pairs are provided, a pair of porous liquid distributing members are disposed generally between the upper frame and the ion selective electrode pairs for communicating the ion selective electrode pairs with the pair of liquid access holes.
In the case where the ionic activity measuring device having the aforesaid configuration is provided with, for example, three sets of the ion selective electrode pairs responding respectively to Na.sup.+, K.sup.+, and Cl.sup.- ions, a reference solution having known activity values of these ions is spotted to one of the pair of the liquid spotting holes, and a sample solution wherein the activity values of these ions are unknown is spotted to the other of the pair of the liquid spotting holes. (The reference solution and the sample solution should preferably be spotted substantially at the same time.) The reference solution and the sample solution penetrate through the porous liquid distributing members to the corresponding ion selective electrodes. The sample solution and the reference solution penetrate to the porous bridge and join near the middle of the porous bridge to achieve liquid junction, and thus electrical conduction is accomplished between the two solutions. As a result, a potential difference arises between the electrodes of each ion selective electrode pair, being proportional to the difference in activity of each ion between the sample solution and the reference solution.
By measurement of the potential difference, it is possible to determine the activity of Na.sup.+, K.sup.+ and Cl.sup.- ions in the sample either simultaneously or separately, based on the calibration curves determined in advance using standard solutions having various activity values of ions (according to Nernst Equation).
With the aforesaid ionic activity measuring device, it is possible to measure the ionic activity simply by spotting the sample solution and the reference solution only once. Therefore, the ionic activity measuring device is very advantageous for analysis of an aqueous liquid sample, particularly for clinical analysis of a body fluid such as blood.
Preferably, the sample solution and the reference solution are fed to the ionic activity measuring device substantially at the same time. Therefore, a need exists for a spotting feed means suitable for the spotting operation. The use of a dual pipette device adapted to drawing-in and ejection of the sample solution and the reference solution with a single device would be particularly convenient as the liquid feeding means for the simple measurement of ionic activity.
The dual pipette device should preferably be constituted so that it has a pair of liquid dispensing tips from which the sample solution and the reference solution are dispensed simultaneously to the pair of the liquid access holes of the ionic activity measuring device. Specifically, the distance between dispensing tips of the dual pipette device should preferably be approximately equal to the distance between the liquid access holes of the ionic activity measuring device for feeding of the solutions to the device.
The distance between the liquid access holes of the ionic activity measuring device is usually very small (less than 1 cm). The distance between the pair of the liquid dispensing tips of the dual pipette device equal to the distance between the liquid access holes of the ion measuring device, which is so short, makes it difficult to draw a sample solution and a reference solution from a blood sampling tube, a reagent bottle or the like respectively into the dropping tips of the dual pipette device.
Particularly, for the measurement of ionic activity in a body fluid, it is desirable that the body fluid taken from the living body should be fed to the ionic activity measuring device so quickly that the body fluid may not be exposed to ambient atmosphere. It is preferred that the dual pipette device directly draw the sample solution from the living body or the like and simultaneously feed the sample solution and a reference solution, which is independently drawn into the dual pipette device to the pair of the liquid access holes of the ionic activity measuring device. However, no such dual pipette device has heretofore been known.